The present invention relates to an impact tool that has a valving arrangement utilizing a sleeve valve that has a controlled displacement during valving operations, and which opens ports to a hammer head to drive the hammer under hydraulic fluid pressure. Pressurized hydraulic fluid is provided by a sliding stepped piston that slides along the valve to initially compress a gas and which piston is then driven by compressed gas to force hydraulic fluid under high pressure against the hammer. The valve mates with a seat and is configured to cushion the engagement of the valve and seat as the valve reaches the end of its stroke. An accumulator is preferably provided for modulating pressure spikes generated by hammer rebound after an impact stroke.
Impact tools are known, as shown in U.S. Pat. No. 6,155,353, issued to one of the present inventors. The '353 patent illustrates a hammer slidably mounted in an outer body and a sliding valve of the general type shown in this specification. The '353 patent includes a piston that compresses a gas that in turn will, when valved, drive the piston to force hydraulic oil under high pressure against the hammer. The hammer then strikes a striking or breaking tool that is used for breaking hard materials such as concrete, asphalt and the like.
The existing hydraulic powered impact tools generally provide hammer impacts on the breaking tool in rapid repetition of short bursts of high energy, and the impact tool oscillates during operation with a high frequency. Various valving arrangements have been advanced, with a goal toward greater energy efficiency. Maximum utilization of input energy for providing output forces of the hammer is desired, and obtaining higher impact forces on the impact tool also is a desired goal.